Part number of the exact thermal pad? Some are adhesive and suitable for mounting of lightweight heatsinks. It seems you have bought this, based on the manufacturer response.
If you got that kind of stuff by accident, then it was good luck, keep buying the same.
If it is the normal stuff and currently gravity is keeping it in place, it will be OK if you keep the thing upright and move it carefully. But it's quite an assumption! At some point, someone will handle it more roughly.
Having some mounting pressure is beneficial for good thermal contact, though. If only lightly touching, gaps of air can remain.